Our overall objective is an increased understanding of immunorecognition and the basis of allogeneic incompatibilities, especially in phylogenetic perspective. Existence of a highly discriminating alloimmunity with a specific memory component has been demonstrated by us in representative species of marine sponges, reef corals and soft corals. Although, at the functional level, immune reactivity in these "lower" animals is surprisingly similar to that found at the mammalian level the underlying mechanism: are only now being discovered. The human immune system is exceedingly complex, involving, in many cases partly understood,interactions of numerous cells and factors. Basic findings in these simpler invertebrate animals could provide important insights in understanding the more elaborate immunologic mechanisms of mammals. Proposed studies would now focus on the following questions in representatives of these invertebrate groups: 1. Sponges: Continuing from current studies that have defined alloimmunity in the sponge Haliclona aquaeductus and the initial characterization of cell types, we will continue to characterize immunocytes and their functions by means of histology, electron microscopy and in vivo and in vitro experiments directed towards critically defining cell populations, interactions, movements, and modes of killing. Preliminary molecular studies will also be initiated if probes and techniques are proven in coelenterates. 2. Coelenterates: Although tissue interactions in the gorgonians (soft corals) have been cited as major examples of invertebrate "immunorecognition", it has only been recently that they have been shown, in our laboratory, to meet the three minimal criteria of an adaptive immune response: 1) cytotoxicity, 2) specificity, 3) a memory component. In this proposal we will continue our studies of the cellular basis for the response using the techniques of in vivo experiments and histological and ultrastructural examinations. In vitro cellular experiments will be started and molecular studies will follow-up our highly promising preliminary findings of possible MHC gene homologies.